1. The Field of Invention
This invention relates generally to systems for sensing environmental or physical parameters such as for pressure, temperature and light changes, and to transducers for generating electrical signals corresponding to such remotely sensed environmental or physical parameters. The invention further relates to an electronically operated CPR force monitoring system.
2. State of the Art
A great many devices are known for sensing force and pressure values. For the purposes of the present discussion, the terms force and pressure can be considered interchangeable, and to include other force related values such as torque. Likewise, devices are known for sensing temperature and light parameter changes. Many of such devices are mechanical in nature, and many are electrical devices. While many of these devices have proven very effective for their intended uses, there remains a need in many areas for compact, reliable, effective, inexpensive and low power sensor and transducer devices and systems. For example, in U.S. Pat. No. 4,858,620,filed on Feb. 28, 1986 and which issued on Aug. 22, 1989, entitled "Warning Systems for Excessive Orthopedic Pressures", a non-invasive system for remotely monitoring the pressure beneath the cast on a part of the body is disclosed for warning when the measured pressure is approaching dangerous levels. That system should incorporate remote sensors which are compact enough to fit beneath the cast without requiring any modification to the cast's size or shape. Furthermore, the system, being battery operated and portable, must be reliable and effective to protect the patient, and still be of low power requirements and inexpensive. Although means are known for measuring pressures beneath casts, among the reasons why such means are not widely used are that they are invasive, difficult to use and their prohibitively expensive, particularly in view of the present absence of such systems in existing orthopedic procedures and because the addition of such systems would significantly increase the cost of the cast. Another medical application requiring a force detection system is a CPR unit in which the force applied to the lower sternum is displayed in real time for each of the cyclic compressions during the procedure. The object, of course, is to prevent forces that are too low to be effective or so high as to cause physical damage to the patient's chest.
Aside from the medical application discussed above, there are other applications where a need exists for low cost, remotely located sensors to be utilized in transducer circuitry. For example, such need exists in the automotive industry. This need is discussed by Flynn, in his article in Product Engineering, August, 1978 (pgs. 43-49).
A number of electrical devices have been developed and described in the patent literature for detecting changes in environmental or physical parameters. One such device is described in U.S. Pat. No. 4,552,028. This patent discloses a single device for measuring force by a capacitive sensor.
U.S. Pat. No. 4,562,382 discloses a solid-state inverter including a multiple core transformer which is useful as a high frequency power source for use in connection with an electron discharge lamb.
In U.S. Pat. No. 4,381,506, a single unit transducer apparatus is disclosed. This apparatus provides an electrical signal which senses motion of a component, e.g., a movable ring about a magnetically conductive core. This apparatus is designed for coupling to internal combustion engines.
In U.S. Pat. No. 4,156,223, an improved positional transducer is disclosed which utilizes an elongated, hollow, cylindrical tube of a magnetically saturable material, a sensing wire that runs through the tube parallel to its elongated axis and a pair of elongated, generally rectangularly shaped magnets of opposite polarity which are closely positioned adjacent diametrically opposite exterior portions of the tube. A similar positional transducer is illustrated in U.S. Pat. No. 3,958,203; however, the '223 patent is an improved version of the transducer disclosed in this patent.
U.S. Pat. No. 4,122,427 discloses a motion monitor particularly useful for monitoring infant respiration. The monitor comprises an oscillator driving an ultrasonic wave generator, a receiver for ultrasonic echoes, a phase detector for detecting phase shift between the outputs of the detector and an oscillator, and means for recovering the respiration envelope from the output of the phase detector.
U.S. Pat. No. 3,140,475 discloses a device for position and motion indication. The device includes a primary coil and a secondary coil coaxially aligned in an end-to-end relation and electrically connected in series, with an A.C. supply connected across the primary coil and a signal readout device connected across both the primary and secondary coils in series relation.
In U.S. Pat. No. 3,020,527, a position indicating system which will indicate the position of a device at a location remote from a movable device is provided. More specifically, a telemetric system is disclosed that may be employed expeditiously with an elongated tube which tube may act as a pressure wall.
U.S. Pat. No. 3,001,183 also relates to position indicator systems for sliding magnetic sleeves which operate within a completely enclosed vessel. Specifically, a remote linear position indicator is disclosed that has a sensing element positioned within a tubular magnetic wall.
U.S. Pat. No. 2,284,364 discloses a tensiometer for measuring thread tension while the thread is passing through the measuring device at a high rate. This device was designed for use in the fiber and garment industries.
U.S. Pat. No. 3,142,981 discloses a transducer device for producing digital electrical signals to measure the magnitude of force applied to the force sensing element. The force sensing element includes a load ring, and a means for applying a force to cause a deformation of the load ring. The patent also discloses employing an oscillator to produce a stable frequency within the frequency range of the oscillator whose frequency varies with the force applied to the load ring.
U.S. Pat. No. 3,206,971 discloses a force measuring apparatus wherein a frequency determining part of an oscillator is coupled to a spring member. The resilient deformation of the spring member caused by the forces to be measured produces frequency changes in the oscillator corresponding in magnitude to the deformation.
U.S. Pat. No. 3,522,858 discloses a snow-depth measuring device which permits measurement of small changes in the pressure of a liquid contained in a factory sealed chamber between two parallel plates, one of which is exposed to the snow fall. Attached to the outer frame of the device is a pressure transducer comprising bellows, a core piece and a coil, all enclosed in a housing.
U.S. Pat. No. 3,727,606 discloses a device for providing continuous monitoring of human respiration and heart rate comprising a fluid-type mattress located in contact with the human and producing pressure signals in response to the breathing and heart rate. A pressure transducer is provided for interpreting the pressure signals for application to an electronic circuit, or visual or audible recognition of the signals.
U.S. Pat. No. 3,791,375 discloses a device for sensing and warning of excessive ambulation force. The device is designed to be worn on a human foot, and may be used during recovery from orthopedic surgery of the lower extremity. The device comprises a fluid-containing load cell which deflects and changes its volume in accordance with the amount of load thereon.
U.S. Pat. No. 4,175,263 discloses a technique for monitoring the movement of an individual from a particular area. The device comprises a sealed fluid filled pad and comprises two distinct fluid areas or pressure sensing areas. Movement of a patient or a child is detected by the change in force or pressure exerted on the fluid.
U.S. Pat. No. 4,208,918 discloses a digital pressure sensor in which a first oscillator is associated with the pressure detector and a second oscillator of the same construction as the first is provided for determining a sampling period of the output signal of the first oscillator.
U.S. Pat. No. 4,324,259 discloses a device for detecting body function changes such as respiration and contractions of a woman in advanced pregnancy and labor. The device comprises a detector capsule having one wall defined by a resilient diaphragm for engagement with the abdominal wall and is connected to a variable volume compartment operably connected to a volume responsive transducer.
German Patent 737,882 discloses a position indicator which includes a movable magnetic sleeve about a core element containing longitudinal windings to vary inductance.
None of these above disclosures, however, teach or suggest the sensing means of the present invention. Also, a remotely located sensor from the transducing means of the type disclosed in the present application is not suggested by the teachings of the above discussed disclosures.
Other applications for pressure and the like monitoring systems, which might well be fulfilled upon the availability of compact, reliable, effective low power, portable and inexpensive remote sensors and associated transducer functions, involve measuring sport related values (e.g., measuring force applied to boxing gloves, boxing bags and running shoes; measuring total energy expended in bicycling; monitoring pressure in ski bindings and ski boots; measuring muscular expansion in a weight lifter); measuring the redistribution of body fluids in space or when subjected to varying and/or extreme gravitational forces; measuring weight; measuring pneumatic tire pressure, etc. Also, such a monitoring system may be useful for the remote monitoring of pressurized containers, e.g., fire extinguishers and gas containers used with analytical instruments and the like, respiration therapy, automotive performance, and monitoring fluid flow and fluid levels in industrial processes, to name a few.